Method for operating a glow plug, and glow plug control device
A method for operating a glow plug by means of pulse-width-modulated voltage pulses which are generated by controlling a load transistor, wherein a heating current flowing through the glow plug is measured and the duty cycle of the pulse-width-modulated voltage pulses is changed in accordance with values of the heating current. The heating current can be measured by means of a current measurement circuit, through which a sense current flows parallel to the load transistor, and the value of the heating current is calculated by multiplying a measured value of the sense current by a kILIS factor, wherein the temperature of the current measurement circuit is measured and the kILIS factor is defined in accordance with the measured circuit temperature. A glow plug control device is also disclosed.
1. A method for operating a glow plug in which the duty cycle of pulse-width-modulated voltage pulses generated by controlling a load transistor is changed as a function of the heating current flowing through the glow plug, the method comprising:
providing a current measurement circuit through which a sense current flows parallel to the load transistor;
measuring the sense current;
measuring the temperature of the current measurement circuit;
defining a kILIS factor as a function of the measured circuit temperature; and
calculating the value of the heating current by multiplying the measured value of the sense current by the defined kILIS factor.
2. The method according to claim 1 , wherein a temperature dependence of the kILIS factor is taken into account with a characteristic curve or at least two different reference values that have been established for different temperatures.
3. The method according to claim 1 , wherein the kILIS factor is defined in relation to the intensity of the sense current.
4. The method according to claim 1 , wherein the current measurement circuit comprises a sense transistor which is connected in parallel to the load transistor and through which the sense current flows.
5. The method according to claim 1 , further comprising measuring electric voltage, calculating a temperature-dependent control variable of the glow plug from the measured voltage value and a measured value of the heating current, and regulating the control variable to a target value associated with a target temperature of the glow plug.
6. The method of claim 5 , wherein the temperature-dependent control variable is resistance of the glow plug.
7. A glow plug control device, comprising:
a plurality of glow plug connection terminals, wherein each glow plug connection terminal is connected in series to a load transistor;
a current measurement circuit connected in parallel to each load transistor;
a data memory which stores calibration data of the temperature dependence of a kILIS factor; and
a control circuit for controlling the load transistors, the control circuit having a temperature sensor for measuring the measurement circuit temperature, the control circuit being configured to:
(a) determine the kILIS factor as a function of a measured value of the circuit temperature,
(b) measure a sense current flowing through the current measurement circuit, and
(c) multiply the measured sense current by the determined kILIS factor to calculate the value of the heating current flowing through the glow plug.
8. The glow plug control device according to claim 7 , further comprising a data connection for reading calibration data or data for calculating calibration data of the kILIS factor.
9. The glow plug control device according to claim 7 , wherein the control circuit is configured to determine the kILIS factor using the stored calibration data.
10. The glow plug control device according to claim 7 , wherein individual calibration data for each load transistor is stored in the data memory.
11. The glow plug control device according to claim 7 , wherein the current measurement circuit is an integrated semiconductor element.
12. The glow plug control device according to claim 7 , wherein the temperature sensor sits on a circuit carrier plate which carries the current measurement circuit.